Since the shooting in Newtown, Connecticut, the debate over gun violence in the Untied States has begun in earnest. Some common talking points can and should be easily dismissed — the idea that regulating access to guns is always unconstitutional or makes tyrannymore likely, to take two examples. But not every argument against expanded gun regulation is ridiculous. There are some, based on the evidence about and history of gun use in the United States, that are worth taking more seriously. You’re likely to hear them a lot over the course of the coming debate. Here’s a list of some of the more commonly made, more serious arguments against gun regulation — and why they fail to effectively make the case against new laws:

These so-called “external features” not only themselves allow for faster rates of fire and other more lethal uses of the guns, but also serve as effective proxy definitions for the sort of weapons best suited to kill people as efficiently as possible. The definition of “assault weapon” in the new federal ban proposed by Senator Dianne Feinstein (D-CA) with respect to semi-automatic rifles and pistols is focused on two kinds of each. The rifles are civilian equivalents of “assault rifles,” the main class of rifle used by modern militaries. “Civilian” versions are distinguished only by their inability to fire either automatically or in bursts without a conversion kit. The pistols have features that make them liable to be converted to full automatic versions (that is, into submachine guns) or otherwise enhance their lethality (e.g., allow for faster rate of fire).

The Feinstein law picks out those sorts of weapons in two ways. First, it bans specific guns (like the AR-15s used by James Holmes in Aurora and Adam Lanza in Newtown) that are particularly deadly. Many of these guns are civilian equivalents of military assault rifles, because — as assault rifle expert C.J. Chivers puts it — these guns were “conjured to form solely for the task of allowing men to more efficiently kill other men” because they are “smaller, lighter in weight, more tactically versatile and require a lighter per-man effective ammunition load than the infantry rifles that preceded them.” The Feinstein provisions, unlike in the 1994 federal ban, specify that “altered facsimiles with the capability of any such weapon thereof” are also banned, so taking out a single screw and calling the weapon something different would not allow manufacturers to skirt the ban. The second provision defines generic features — like barrel shrouds that allow for faster fire or (for pistols) magazines outside the pistol grip — and bans any gun that has more than one of them and a detachable magazine (the old ban allowed a maximum of two features, making it easier to skirt).

These aren’t merely cosmetic features: they’re the ones that mark guns optimized for effective performance in combat-style situations. They also mark guns easily convertible to full automatic fire, like the TEC-9 submachine guns once favored in gang killings. One such kit is fully legal, despite the 1934 National Firearms Act banning the possession of automatic weapons without a permit. The kit produced by the company Slide Fire product allows you to turn your AR or AK series assault rifle into a rapid-fire machine without technically running afoul of the federal definition of “machine gun.”

The notion that assault rifles are similar in caliber to hunting rifles, and hence no more dangerous, doesn’t stand up to scrutiny for similar reasons. As the California Attorney General’s office explains, “Caliber has no bearing on a weapon’s status as a series weapon and should be disregarded when making an identification. For example, upper receiver conversion kits are available to convert almost any AR series weapon into .45 ACP, .40 S&W, 7.62 X 39 mm, 9 mm, 10 mm, or .223 caliber.”

There is evidence that the 1994 federal ban saved lives despite a series of loopholes closed in the Feinstein bill and several state bans. Though there isn’t reliable data on the number of people killed by assault weapons in the United States, there is strong evidence from the Mexican border that both California’s assault weapons ban the federal assault weapon ban lowered the homicide rate. The clearest comes in a 2012 academic paper that treated the expiration of the federal assault weapon ban in 2004 as a natural experiment — California still had its assault weapon ban, but Texas, New Mexico, and Arizona didn’t have equivalents. The authors tracked homicides and weapon seizures in the Mexican provinces bordering the states, finding disproportionately lower homicide rates in provinces near California. This difference remained when other potential causes (like police presence) were accounted for, suggesting the federal and California bans had successful kept assault weapons out of the hands of cartels and other criminals. The expiration of the federal law, on this paper’s model, has gotten roughly 239 people killed on the Mexican border per year since 2004. This is consistent with another paper that found “the expiration of the AWB is responsible for at least 16.4 percent of the increase in the homicide rate in Mexico between 2004 and 2008.”

The 1994 ban, according to a Department of Justice review, also appears to have caused the percentage of crimes involving assault weapons in some major US cities to drop from 72 percent to 17 percent.

The reality is that even a minor percentage decline in fatalities could means hundreds of fewer people killed per year. Estimates about the percentage of crimes involving assault weapons range from two to eight percent. But if the Feinstein law could make a dent in that number, that’s still a big deal. Consider one estimate, based on federal gun trace data, that the original federal assault weapons ban reduced the national percentage of gun crimes involving assault weapons from about five percent to about two percent. Assuming that, because assault weapons are rarer and deadlier and hence more likely to be responsible for homicides, this translated to a one percent decline in the homicide rate. That’s 110 fewer murders per year given the roughly 11,000 Americans killed by gun homicide every year. We can debate whether would-be murderers would simply use other types of guns, and whether they’d be as deadly, but the point is that even a small percentage drop in gun homicides nationwide would be a huge victory.

This one is just an abuse of statistics — just because violence is declining doesn’t mean it couldn’t be declining faster. It’s true that violent crime as a whole, including gun homicides, has declined over the course of the past decade. This suggests that gun laws aren’t the only factors that determine the crime rate — see Kevin Drum’s fantastic series on lead and crime for a clear explanation of the other causes that might’ve mattered.

Moreover, when you compare different states with different gun laws at the same time, you find states with tighter gun regulations (including assault weapon bans) have significantly lower rates of firearm death. This suggests that, independent of whatever good fortune the United States has seen the past decade, better gun laws could significantly accelerate decline in lives lost to gunfire.

UNIVERSAL BACKGROUND CHECKS AND DEALER INSPECTIONS

First, some mass shooters do have criminal or worrisome mental health records, like James Holmes and Seung-Hui Cho. Both Holmes and Cho bought their weapons legally. Cho even passed a background check despite being ruled “an imminent danger to himself because of mental illness” because of Virginia’s lax standards about what counts as a red flag for purposes of a background check.

Second, there’s another kind of mass murder — the 11,000 gun homicides per year — that improving our background check and inspection system could unequivocally help prevent. One percent of gun dealers sell half of the guns used in crimes nationally, which other evidence indicates have been deterred in the past by stepped-up ATF enforcement. Domestic violence perpetrators, people with substance abuse problems, and individuals convicted of other violent crimes are all more likely to commit firearm crimes, yet they can freely purchase a weapon in a private sale at, say, a gun show, no questions asked. In a finding that should surprise no one, 80 percent of firearms used in crimes appear to have been purchased privately. State and city-level comparisons indicate that “states which do not regulate private gun sales, adopt permit-to-purchase licensing systems, or have gun owner accountability measures, like mandatory reporting of gun thefts, export significantly more guns used by criminals to other states that have constrained the supply of guns for criminals by adopting strict gun sales regulations.”

It’s hard to estimate a specific number of lives that would be saved by requiring background checks on all sales, requiring all states and federal organizations to input criminal and drug records to the National Instant Criminal Background Check System (they don’t have to, currently), and giving the ATF more power to trace and sting “bad apple” gun dealers and traffickers, but this mountain of evidence suggests that the effect of such measures could be substantial.

Background checks are hardly onerous and likely won’t “unjustly” disqualify that many people. A check usually process very quickly at the point-of-sale and even abnormally long wait times top out around five days. It’s hardly an excessive burden for someone seeking a deadly weapon they’ll then be able to own for life.

But does current federal law unfairly bar certain groups of people from acquiring guns? Currently, only one percent of sales are blocked by background checks, the vast majority of which because the purchaser has committed or been indicted for a felony, is a fugitive from justice, or is a perpetrator of domestic violence. Presumably, both the percentage and absolute number of people denied would go up if the background check system were improved, but the breakdown suggest that only a minute number of (for example) harmless, recreational drug users would have their access to guns restricted because they failed a drug test.

Moreover, it’s critically important that felons be restricted from accessing firearms. The New York Timessurveyed felons and people convicted of “domestic violence misdemeanors” who (as a consequence of state-level, NRA-backed legislation loosening restoration standards) regained their gun rights. It found that 13 percent went on to commit crimes, half of which were felonies. As the Times notes, there’s also evidence that denying handguns to people arrested for or convicted of felonies reduces their likelihood to commit future crimes by 20 to 30 percent.

It is almost certainly true that universal background checks and a more complete database of disqualified persons will lead to less people being able to buy guns legally. Some fraction of them likely wouldn’t commit crimes — your average pot smoker isn’t the violent type. But the misguided excesses of the war on drugs shouldn’t obscure the fact that, right now, domestic abusers, violent felons, gang members, and drug addicts can buy guns with impunity. The evidence is very clear that members of these groups are more likely to commit gun crimes and that improved background checks can limit their ability to do so, saving lives in the process. A minor limitation on a tiny percentage of Americans’ ability to buy guns seems like a trade-off that’s easily worth making in light of America’s gun homicide rate.

HIGH CAPACITY MAGAZINES

There are plenty of large capacity magazines that aren’t more likely to jam that could majorly amplify the death toll in a mass shooting. While it’s true that 100-round magazines are more likely to jam, most high-capacity magazines aren’t nearly that large, and hence can use mechanisms that don’t appreciably increase the risk of jamming. The modern US Army M-16, for example, has a 30-round magazine, as does a standard AK-47 (a gun famous for jamming rarely). And as magazine technology improves, larger magazine sizes become more practicable: as Josh Sugarmann, executive director and founder of the Violence Policy Center, told ThinkProgress, evidence “from gun magazines and industry publications [suggests] the trend is towards higher capacity magazines.”

The Feinstein law, then, bans magazines that hold more than ten bullets for a reason. Suppose a shooter had the same assault weapon, but had four magazines or clips that could hold thirty rather than ten bullets. That shooter would have 80 more bullets, or three times the number, than he would have without the high-capacity magazine ban. Since magazine size doesn’t make much of a difference for how many magazines an individual shooter could carry on their person, limiting access to high-capacity magazines could result in a shooter carrying significantly fewer bullets — and hence being able to fire at significantly fewer people.

Not only is this assertion dubious on its face, but it’s bad justification for making policy given how rare defensive gun use is. Presumably someone who’s attacking a school or a family would have more people to shoot, and hence require more bullets than the people trying to stop just him. But debating the nuances of this very specific hypothetical situation misses the point broader point that it doesn’t make sense to fixate on these extraordinarily uncommon cases.

The often-cited number that guns are used defensively 2.5 million times a year in the United States is mathematically impossible (more on that later). A survey of criminals who had been shot in a Washington, DC jail indicated that, far from being injured by their victims, they had almost all been hit by other criminals. These data suggest, when combined with other evidence, that defensive gun use is quite rare: “to believe fully the claims of millions of self-defense gun uses each year would mean believing that decent law-abiding citizens shot hundreds of thousands of criminals. But the data from emergency departments belie this claim, unless hundreds of thousands of wounded criminals are afraid to seek medical care. But virtually all criminals who have been shot went to the hospital, and can describe in detail what happened there.”

Defending one’s family is surely a legitimate use for a gun, but the fact that a high-capacity magazine *might* be useful in some subset of these already-exceptional cases isn’t a good reason to permit their widespread ownership if keeping them legal also comes with real, identifiable costs in human lives.

It very likely the ban reduced the supply of high capacity magazines to criminals and a decent chance it prevented unnecessary deaths. While it’s hard to separate the effects of federal and state high-capacity magazine bans on crime from assault weapons bans (they’re generally enacted at the same time), there is excellent evidence that the federal ban on high-capacity magazines ended up restricting access to them. The Washington Posttracked police seizures of high-capacity magazines in Virginia during and after the federal assault weapons ban was in effect. The Post‘s reporters found a steady decline in number of magazines recovered from 1994-2004 (when the law was in effect), but saw the trend halt and then reverse after the ban expired, indicating more criminals were getting high-capacity magazines. One gun expert who was “skeptical” that the federal ban worked said the Post’s evidence changed his mind; its data was “about as clear an example as we could ask for of evidence that the ban was working.”

There is also some old, very tentative evidence that “that victims killed with guns having large-capacity magazines tend to have more bullet wounds than victims killed with other firearms, and that mass murders with assault weapons tend to involve more victims than those with other firearms.” While this evidence is, again, rudimentary, it suggests that a renewed, effective ban on high-capacity magazines might very well save more lives.

THE SCIENCE ON GUNS

The “guns reduce crime” argument gets made in two ways, often together: 1) the presence of more guns deters crime and 2) concealed carry laws allow citizens to stop crime where they encounter it. The two main sources cited for these claims are John Lott’s More Guns, Less Crime, and a series of papers written by Gary Kleck and Marc Gertz suggesting that Americans used guns defensively 2.5 million times per year.

The overwhelming consensus among scholars is that Lott, Kleck, and Gertz are wrong. In a blockbuster article after the Newtown shooting, Salon‘s Alex Seitz-Wald reviewed this research in great detail, finding a series of glaring methodological flaws and a wealth of evidence suggesting more guns led, in fact, to more gun death. It’s really worth reading Seitz-Wald’s piece in full, but to summarize a few salient points: Lott has been unable to produce the survey data supporting his major claim about guns and concealed carry reducing crime, while independent reviews of the evidence have come to opposite conclusions. Kleck and Gertz fail to account for the fact that people often falsely self-report as using guns defensively when they’re actually intimidating people a la George Zimmerman and the Kleck-Gertz numbers mathematically require assuming “burglary victims use their guns in self-defense more than 100 percent of the time,” among other problems.

This argument is mistaken as a matter of both statistics and law. While a simple glance at rough homicide rates suggests very little difference in crime rates between cities with strict gun laws and those without, the relevant research strongly suggests that ease of acquiring guns legally increases the local gun homicide rate. A 2001 paper by Mark Duggan estimated county-by-county gun ownership, finding that counties with higher rates of gun ownership had higher gun homicide rates. A second paper, which used a different measure of gun ownership, came to a similar conclusion. Both papers found that only gun homicide rates — and a county’s other homicide or broader crime rates — is affected by gun ownership, suggesting that easy access to guns increases gun homicide by getting more guns to more people.

A third, more recent paper goes further, finding that gun ownership increased gun homicides even when you control for levels of urbanization and poverty. That is, cities with more guns, all other things being equal, will have more homicide deaths, as will poorer areas. This points to the basic statistical error in the “what about Chicago?” argument — the question isn’t whether gun regulation is the only or principal determinant of gun homicide rates, it’s whether there’d be more or less gun death in Chicago if Chicago and nearby counties did a better job restricting access to guns. Given that states with tighter gun laws also have less guns (and less gun deaths), it seems the same would hold true (again, if you hold other variables like poverty and overall crime rate constant) on the city-to-city level. Moreover, studies of cities with strong background check and illegal sales enforcement provisions have found clear evidence that imposing these measures lowered the number of guns being diverted to criminals.

There’s another, well-known problem with this conceit — lax federal and state laws make it easy to purchase guns from nearby, underregulated counties or states and bring them into cities. In Chicago, for example, gun sellers will simply set up shop just outside the city limits and sell to traffickers who bring the weapons into the city. That’s one of the key arguments for the sort of federal action being considered today, especially universal background checks at nearby gun shows to prevent this sort of trafficking. A uniform federal standard would make it much harder for criminals to take advantage of state and local variation.